The present invention relates generally to bond pads fabricated on a semiconductor die. More specifically, during formation of a bond pad, a barrier layer is deposited over the metallization layer, the barrier layer is masked, and subsequently both the barrier layer and the metallization layer are etched in one step. Thereafter a bonding layer is formed over the barrier layer, preferably using an electrolysis process.
In the field of semiconductor devices, producing simple, reliable, and inexpensive bond pads is a primary concern of manufacturing. Bond pads are wired to device elements located in the semiconductor die substrate and provide exposed contact regions of the die which are suitable for wiring to components external to the die. In one typical case, a bonding wire is attached to the bonding pad at one end and a portion of the lead frame at the other. Any improvement which simplifies the manufacturing process, enhances the reliability, or reduces the costs of bond pads can provide a competitive advantage to those involved in the commercial manufacture of semiconductor devices.
One common, simple, and inexpensive bond pad is just an exposed aluminum portion. A gold bonding wire is bonded to this aluminum pad. When ambient temperatures are less than approximately 150.degree. C., the physical attachment and the electrical connection between the gold wire and the aluminum pad are sufficiently reliable. However, when temperatures rise above 150.degree. C., the bond rapidly degenerates due to the growth of gold and aluminum intermetallics. That is, the two metals start to diffuse between each other and begin forming aluminum-gold chemical compositions. As a result, porosity, delamination, and voiding occur within the bond. Time lapse and increased temperature tend to worsen this relationship, and the bond will eventually fail. Consequently, potential reliability problems prevent using the aluminum bond pad under conditions where the ambient temperature is known to exceed 150.degree. C. Furthermore, even when the ambient temperature is less than approximately 150.degree. C., the aluminum bond pad is susceptible to corrosion simply because it is exposed.
One prior art solution to this problem is discussed with reference to FIG. 1. Initially, an aluminum metallization layer 12 is deposited over the entire wafer 10. This metallization layer 12 is then masked and etched, thereby providing regions of the metallization layer 12 which are electrically connected to device elements in the substrate 10. Next, a non-conductive layer 14 is deposited conformally over the entire wafer. The non-conductive layer 14 is also masked and etched, providing an exposed region of the metallization layer 12. Then, a barrier layer 16 is deposited over the entire wafer. Finally, a gold bond layer 18 is deposited by reactive sputtering over the entire wafer, and, gold bond layer 18 and barrier layer 16 are simultaneously masked and etched so that only the previously exposed regions of the metallization layer are covered. Thus the gold bonding wire can be connected directly to the gold bond layer 18 which is in electrical contact with the metallization layer 12. The barrier layer 16 is made of a material which prevents intermetallics from forming between the metallization layer 12 and the gold bond layer 18.
Although the aforementioned method prevents the intermetallic degradation of the bond pads and corrosion of the metallization layer, it has generally not been implemented in wide scale production. This is due to the numerous manufacturing steps required and the high cost of material. Note that there are three costly mask and etch steps required in this process. This is one more than typically necessary for the aluminum bond pad. Additionally, because of the gold etching step, much of the gold used in this process is neither used in the final product nor can it be reclaimed. What is required is a process which effectively caps the metallization layer in a more cost effective manner.